The present invention relates to the identification of compounds which deter feeding by insects and in particular such compounds which are structurally related to xylomollin, a naturally occurring feeding deterrent.
Heavy use of insecticides presents environmental dangers and promotes the development of resistant insect populations. One alternative to present practices relating to insecticide use involves the application on crops of chemicals which inhibit or deter feeding thereon by insects. Use of naturally occuring feeding deterrants and their derivatives for crop protection is appealing because such compounds do not need to be toxic to work and therefore the additional concerns of toxicity to other animals, and in particular to mammals, are avoided. Folklore and stories of traditional farming practices are replete with references to feeding deterrent or repellent properties of plants. A well known practice involves the placement of hedge apples in the corners of basements or root cellars to repel crickets and other insects, spiders and even some rodents.
Extracts from plants known to exhibit antifeeding activity have been used in compositions developed for commercial utilization. For example, U.S. Pat. No. 5,290,557 to Mason et al. discloses the use of saponin containing extracts of Yucca schidigera as an antifeedant to control terrestrial molluscs. Similarly, U.S. Pat. No. 4,676,985 to Gould et al. discloses a process of protecting crops from damage by coating seeds or seedlings with an extract from plants having feeding deterrent activity such as extracts from butterfly milkweed, English ivy, santolina, bergamot, clary and swamp milkweed.
Others have focused on identifying derivatives of naturally occuring insect feeding deterrants which also exhibit feeding deterrant activity and which can be synthesized commercially. U.S. Pat. No. 5,047,242 to Klocke et al. identifies derivatives of azadirachtin which exhibit antifeedant activity. Azadirachtin is a naturally occuring feeding deterrant which can be isolated from the seeds of the neem tree and from the fruits of the chinaberry tree. U.S. Pat. No. 4,960,791 to Klocke et al. identifies antifeedant derivatives of salannin which is a naturally occuring insect antifeedant related to azadirachtin. U.S. Pat. No. 4,855,319 to Mikolajczak et al. discloses use of asimicin as a feeding deterrent. Asimicin is a derivative of tetrahydrofuranoid acetogenins, which are characteristic of the Annonaceae plant family and known feeding deterrants.
As of yet, it does not appear that any of these compositions have achieved wide-spread commercial use or success. The lack of commercial success of such compositions may be due to the relative high cost in obtaining large quantities of the specified plant extracts or in synthesizing the relatively complex chemical derivatives of naturally occuring antifeedants identified to date. Derivatives of naturally occurring feeding deterrents still provide a promising avenue for alternatives to currently available insecticides for use in integrated pest management programs. The compounds should be ecologically sound and non-toxic to mammals. The synthesis of these compounds should be relatively inexpensive and result in the production of relatively stable compounds with the minimal structural components necessary for relatively high activity.
Xylomollin, which has the following chemical formula: ##STR1## is found in the unripened fruit of the East African tree Xyloccarpus molluscensis (Meliaceae) and has been previously identified as a potent feeding deterrent. However, due to the complexity of xylomollin's chemical structure, currently known methods of synthesizing xylomollin are prohibitively expensive for commercial purposes.